Pd/Cu bimetallic nanoparticles embedded in macroporous ion-exchange resins: an excellent heterogeneous catalyst for the Sonogashira reaction† Debasish Sengupta, a Jony Saha, b Goutam De * b and Basudeb Basu * a Cationic and macroporous amberlite resins with formate (HCOO  ) as the counter anion (ARF) have been used to prepare a new class of heterogeneous Pd/Cu bimetallic composite nanoparticles (NPs) (Pd/Cu– ARF). The physicochemical characteristics of Pd/Cu–ARF were examined with the help of FTIR spectroscopy, X-ray powder diffraction (XRD), transmission electron microscopy (TEM) and atomic absorption spectroscopy (AAS). XRD and TEM showed the existence of composite NPs made of metallic Pd, PdO and CuO. The TEM analysis revealed fairly uniform distributions of composite NPs of average size 4.9 nm. The as-synthesized nanocomposite material (Pd/Cu–ARF) exhibited high catalytic activity in the Sonogashira cross-coupling reaction between aryl iodide and terminal alkynes. Heterogeneity of the catalytic activity was evidenced from different tests (hot-filtration and catalyst-poisoning experiments) and the recycling ability of the catalyst was examined for five consecutive runs without any significant loss of activity. Introduction Owing to a high surface-to-volume ratio, metal/metal oxide nanoparticles (NPs) exhibit potential catalytic activity for diverse organic and inorganic reactions. 1 Bimetallic nano- particles, composed of two different metals, oen show improved catalytic performances and nd applications in several industrial processes, primarily in fuel industries or environmental catalytic processes, and more recently in C–C cross-coupling reactions. 2 Bimetallic catalysts represent an interesting class of catalysts because one metal can tune and/or modify the catalytic properties of the other due to the electronic and structural interactions. 3 They are also of importance because of the modication of their surface electrons relative to that of the individual metals. 4,5 There has been considerable interest in the formation, structure and further exploitation of the catalytic activity of bimetallic particles. 6,7 It has been oen seen that metals interacting with either another metal or metal oxide at the nano level can form nanocomposites with superior activities not seen in bulk alloys. 8 Functionalized solid supports like polymers loaded with metal nanoclusters are now well established as heterogeneous catalysts in cross-coupling reac- tions. 2 From the standpoint of the reduction of environmental burdens and cost effectiveness, nanometal catalysts embedded in/on insoluble supports with ligand-free and minimal or no leaching are highly desirable. However, procedural simplicity, uniform dispersion, cheaper and robust polymeric surface, higher efficiency and life-cycle remain the major challenges for a heterogeneous catalyst. On the other hand, several metal-catalyzed cross coupling reactions require the presence of another metal either as a co- catalyst or to help control the overall process. Representative examples include: (i) Pd-catalyzed Heck coupling reaction in the presence of Ag salts, that is believed to occur via cationic mechanism and oen has a profound effect in controlling the regio- and stereochemistry of the coupled product, 9 (ii) Sono- gashira reaction between an aryl halide and terminal alkynes requires a combination of Pd and Cu as the catalysts, where Cu + plays a catalytic role in transferring the alkynyl group to Pd, 10 (iii) in the Stille coupling reaction, the accelerating effect of CuI on the Pd-catalyzed coupling of aryl iodide and organostannane derivative has been quantitatively evaluated. 11,12 The excellent redox properties of the Pd/Cu system are due to the electron donor and acceptor character of Cu and Pd, respectively. 13,14 The pronounced “Cu-effect” in the Pd-catalyzed cross-coupling reaction 15,16 has stimulated the development of several hetero- geneous bimetallic NPs using commercially available insoluble a Department of Chemistry, North Bengal University, Darjeeling 734013, India. E-mail: basu_nbu@hotmail.com; Fax: +91 353 2699001; Tel: +91 353 2776381 b CSIR-Central Glass & Ceramics Research Institute, 196, Raja S. C. Mullick Road, Jadavpur, Kolkata 700032, India. E-mail: gde@cgcri.res.in; Fax: +91 33 24730957; Tel: +91 33 23223403 † Electronic supplementary information (ESI) available: Powder XRD, SEM images, 1 H& 13 C NMR spectral data, scanned copies of NMR spectra and comparative chart highlighting improved catalytic performance of Pd/Cu–ARF(II). See DOI: 10.1039/c3ta14916a Cite this: J. Mater. Chem. A, 2014, 2, 3986 Received 27th November 2013 Accepted 17th December 2013 DOI: 10.1039/c3ta14916a www.rsc.org/MaterialsA 3986 | J. Mater. Chem. A, 2014, 2, 3986–3992 This journal is © The Royal Society of Chemistry 2014 Journal of Materials Chemistry A PAPER